1. Technical Field
This invention relates to liquid crystal displays (LCDs), and, more particularly to a method for etching indium-tin-oxide (ITO) electrodes and lines using self-assembled monolayers. More specifically, it relates to an etch barrier for indium-tin-oxide, a process for forming an etch pattern on a layer of indium-tin-oxide, and a method for preparing a stamp for transferring an etch barrier material.
2. Background Art
Flat panel displays have become increasingly important in computer industries and in other industries where the display of information is important. These types of displays provide unique opportunities for lowering the weight, size and eventually the cost of displaying information. Thin film transistor-liquid crystal displays (TFT-LCDs) seem to hold the most promise as the technology which will eventually be utilized in almost all practical flat panel displays. Considerable success has been achieved in small size color flat panel displays for consumer electronics as well as larger size color flat panel displays used in notebook or laptop computers.
A TFT-LCD device is made up of two substrates. One contains color filters and the other has TFT arrays. Since ITO is transparent and conductive, it is employed as an electrode or as a conductor on both substrates. It is important to be able to make a desired pattern of the ITO in modern displays. Conventionally, a photoresist and its lithographic processes are used to pattern the ITO. There has been a long felt need for a simplified process to pattern ITO, which will lower the manufacturing cost.
An alternative approach to lithography has been published by Kumar and Whitesides in Appl. Phys. Lett. 1993, 63, 2002-2004. In this process, known as microcontact stamp lithography, stamps are fabricated by casting a replica in poly (dimethylsiloxane) (PDMS) of a master with a negative of the desired pattern. The PDMS stamp is inked with hexadecanethiol, and transferred to gold substrate by transient contact between the stamp and the gold substrate.
The thiol covalently binds to the gold substrate, preventing spread of the bulk liquid phase and thus confining the transferred monolayer to the region of contact. The presence of these thiols allows subsequent lithographic processing of the gold using a cyanide/oxygen etch that selectively removes gold not protected by a monolayer of hexadecanethiol. But its scope is limited to special subset of useful materials, i.e., thiols and gold. In PCT WO 97/06012 and WO 97/06013, Biebuyck and Michel described a detailed method for application in electronic devices.
Self-assembled monolayers (SAMs) are thin organic monolayers of molecules having end groups selectively adsorbed to solid surfaces (R. G. Nuzzo and D. L. Allara, Journal of American Chemical Society vol. 105, pp. 4481-3, 1983). The solid is usually an inorganic material or a metal. SAMs of thiols adsorbed on gold have ordered structures, and their methylene (CH2) groups have all trans configurations. SAMs of n-octadecylsilane were prepared on glass surfaces using hydrolyzed n-octadecyltrichlorosilane (J. Sagiv, Journal of American Chemical Society, vol. 102, pp. 92-98, 1980) or hydrolyzed n-octadecyltrimethoxysilane (C. R. Kessel and S. Granick, Langmuir, vol 7, pp. 532-538, 1991).